Siemens SIPAN 32 Instructions De Service page 85

Dispositif de mesure de conductivité SIPAN 32
C79000-B5477-C045-02
MPIP sarl - 94, rue Mohamed Tounsi - 16013 - ROUIBA - ALGERIE
Tél./Fax : 021 81 11 22 - GSM : 070 91 75 15 ou 072 900 654 - E-mail : mpip@mpi-dz.com
Control takes place with the central process control system PLS or with
a PC when requirements are low. As a rule the functions signal
conversion DP--PA, bus feeeding and bus termination are combined in
a coupling module. A DP/PA coupler or a more powerful DP/PA link for
higher requirements is used depending on the number of PROFIBUS
PA field devices to be operated in the automation system. For
transmission--technical reasons, a terminating resistor T must be fitted
to the remote end of the bus. When using the recommended bus cable
(see section 4.8.12 "Technical data") the theoretically possible line
length (sum of all line distances) is a maximum 1900 m. However, the
current requirements of the individual users and the voltage drop at the
cable must also be taken into account in the planning. The individual
field devices FD can be connected at almost any point in the bus
system. See the "PNO Guide PROFIBUS PA"/1/ for further information.
The DP/PA coupler or DP/PA link are supplied by a power supply unit
with safety--extra--low--voltage (SELV). This power supply must have
adequate reserves to be able to bridge temporary mains interruptions.
The maximum number of devices connected to a bus line depends
on its current consumption and the respective application conditions. The
couplers/links can feed up to 400 mA into the bus in the safe area.
When operating in hazardous areas the intrinsic safety is only
guaranteed if the maximum power supply fed into the bus does not
exceed certain voltage and current values. These are usually:
EEx ia IIC current Is < 90 mA, voltage Uo < 15 V
Mise en service et fonctionnement
4-39